1. Technical Field
The present invention relates generally to aerosol products and methods of making aerosol products. There is a desire to reduce the VOC content of aerosol products, while retaining desired spray characteristics.
2. Description of the Related Art
Aerosol containers have been popular since their inception, because of their marked ease of use and variety of applications. The term “aerosol” includes products that can be dispensed in a stream, spray, powder, gel, or a foam. Innovations in this area of technology have enabled aerosol products that contain organic solvents or water or combinations thereof, as well as products that foam upon ejection and products that delay foaming after ejection. In a typical aerosol dispenser, a container contains a liquid product (also called an “aerosol formula concentrate”) and one or more pressurized propellants that pressurize the product and drive the product out of the container when desired.
The particular pressure of the contents of the aerosol container is important. First, there are practical limitations that relate to particular products used in aerosol containers. Depending on the aerosol dispenser's contents, pressure will affect such considerations as particle size, foaming capabilities, and the ability to evacuate the dispenser's contents completely. Second, there are regulatory constraints set by the government, industrial associations, or other authorities for safety or other reasons. For example, the United States Department of Transportation (“DOT”) regulations dictate the maximum pressure of aerosol containers at 130 degrees (Fahrenheit) for a given type of container. See 49 C.F.R. §173.306. Because of these constraints, the right balance of propellants should be used in order to achieve the desired characteristics of the dispensed product and maximize the amount of product that is capable of being dispensed, while observing the DOT's pressure limits.
Typically, two types of propellants used in aerosol dispensers are liquefied gases and compressed gases. In the aerosol industry, liquefied gases that are used as propellants can include liquefied petroleum gases (“LPGs”) and hydrofluorocarbons (“HFCs”). As used in the context of this patent, the term “liquefied gas” is used to encompass both LPGs and HFCs. In the aerosol industry, LPGs include hydrocarbon propellants (e.g., propane, n-butane, isobutane), and in the context of this patent, the terms “LPG” and “hydrocarbon propellant” are used interchangeably. In the aerosol industry, HFCs include 1,1 difluoroethane (CH3CHF2), known in the aerosol industry as “152a,” and 1,1,1,2 tetrafluoroethane (CF3CH2F), known in the aerosol industry as “134a.” In the context of this patent, the terms “HFC” and “hydrofluorocarbon propellant” are used interchangeably. Compressed gasses have included nitrogen, carbon dioxide, and nitrous oxide.
The use of a compressed gas alone as a propellant has drawbacks, in certain applications, where the pressure is not sustained over the use of the aerosol container; the contents are over-pressurized at the beginning of the consumer's use and become under-pressurized prior to the complete use of the product. The amount of compressed gas retained in a product is dependant on its solubility in the product being dispensed. The less soluble the compressed gas is in the product, the more compressed gas is retained in the vapor phase (i.e., the headspace) within the aerosol container. “Thus, internal vapour pressure of the aerosol dispenser diminishes as the contents are depleted, causing changes in the rate and characteristics of the spray,” U.S. Patent Application Pub. No. 2007/0231290, at [0006] (filed Mar. 31, 2006) (“Robinson”), which is the case where nitrogen is used as the compressed gas. In particular, the use of nitrogen as a compressed gas propellant has been discouraged in the art because of nitrogen's insolubility in the product; this insolubility causes rapid pressure depletion and changed spray characteristics, and for these reasons nitrogen generally has limited applications as a compressed gas propellant in the aerosol industry.
The addition of LPGs and/or HFCs contributes to the aerosol product's desirable spray characteristics. More specifically, certain types of liquefied gases allows the product to foam upon dispensing. However, the use of LPGs or HFCs alone in typical formulations known in the art has its own drawbacks concerning cost and environmental profile, as discussed below. Despite these drawbacks, liquefied gases are presently used as propellants in many aerosol products because of the desirability of foaming aerosol products. In order to foam upon dispensing, aerosol products must contain liquefied gas; for this reason, liquefied gas—whether LPGs, HFCs, and blends thereof—is used in the aerosol industry as the propellant in a variety of foaming aerosol products.
As mentioned above, certain concerns influence the use of LPGs. First, the use of LPGs has significant environmental concerns, as LPGs fall within a class of chemicals known as volatile organic compounds (“VOCs”). VOCs are precursors of ground level smog, which is a significant daily environmental hazard in many urbanized areas. On an individual level, VOCs have been associated with a variety of health problems, ranging from irritation to chronic problems. From a manufacturing standpoint, VOC content in aerosol dispensers is regulated by state and regional governmental entities such as the California Air Resources Board (“CARB”), to name one example, and is also Federally regulated by the United States Environmental Protection Agency (“EPA”). While CARB regulations apply to VOCs—including LPGs—HFCs such as 134a and 152a are not considered VOCs. Thus, 134a and 152a are often looked to for VOC reduction in the aerosol industry today. Nonetheless, the use of 134a and 152a presents different environmental concerns, as 134a and 152a have high global warming potentials (GWP). (By comparison, LPGs have a very low GWP and compressed gases have essentially a zero GWP.) Presently HFCs remain the most costly propellant, followed by LPGs, while compressed gasses are the least expensive in the array of options.
For these reasons, there is a desire to use as little liquefied gas as possible, while still achieving an optimal internal pressure, in order to ensure that the aerosol product can be satisfactorily used (e.g., it can foam upon dispensing) while minimizing the environmental and health hazards of VOCs.
Various methods have been developed in an attempt to reduce the VOC content of aerosol dispensers, while retaining the benefits associated with liquefied gas use. See, e.g., Robinson at [0009] to [0015]. For example, Robinson is directed at reducing VOC content in aerosols. Robinson identifies several of the problems associated with simply reducing the VOC content in aerosol containers. Robinson states that reducing the level of liquefied gas in aerosol dispensers can result in excess product retention in the container, increased particle size in the dispensed product, or a premature reduction in spray rate, all of which affect the performance and desirability of aerosol dispensers. Robinson notes that acetone solvents and microemulsions, or a reconfiguration of the aerosol dispenser hardware, have been used to attempt to reduce VOC content with mixed success. Robinson attempts to address VOC content issues by using a single phase aerosol composition that uses liquefied gas propellants.
Unlike the methods and devices taught in Robinson and other disclosures, it has been found that a reduction of VOC levels contained in aerosol dispensers, while retaining spray characteristics, can be achieved by using both compressed gas and liquefied gas. As discussed above, typically aerosol dispensers use either compressed gas or liquefied gas in order to propel the contents from the container, but the use of both compressed gas and liquefied gas, while maintaining spray characteristics such as foaming capabilities, is new. The use of liquefied gas allows the product to retain desired spray characteristics (e.g., foaming capabilities), while the use of compressed gas allows the manufacture of aerosol containers whose propellants contain less liquefied gas (and hence less VOCs and/or less greenhouse gases), while maintaining adequate pressurization for propellant purposes.
Additionally and/or alternatively, additional pressurization can be achieved by the particular sequence of adding particular components to the aerosol container. In the context of this patent, the terms “filling” and “gassing” are used interchangeably, to refer to the introduction of propellants into the aerosol container. In one sequence of gassing, after the desired aerosol formula concentrate or concentrates are introduced into the aerosol container, liquefied gas is added to the aerosol container, and then the compressed gas is added. A second sequence of gassing is done by adding compressed gas to the aerosol container (after the desired aerosol formula concentrate or concentrates are introduced into the container), and then adding the liquefied gas. One benefit of using the second sequence of gassing is that ambient and elevated temperature pressure increases are achieved that are higher than each of the individual pressures of the liquefied gas and compressed gas, due to the mutual insolubility (or low solubility) of the liquefied gas, compressed gas, and aerosol formula concentrate in each other. In both of these gassing sequences, nitrogen works well as the compressed gas, due to its inert and insoluble characteristics. Other compressed gases, such as carbon dioxide and nitrous oxide, may also be used, but these specific compressed gases present various manufacturing constraints and container corrosion issues when used in water-based aerosol formula concentrates.
By requiring less liquefied gas, the aerosol products not only cost less to produce, but they also contain and release less VOCs when used, which provides obvious environmental, health, and regulatory benefits. And, these aerosol products retain desired spray characteristics, such as the ability to foam upon dispensing.